The present invention relates generally to the field of medical imaging, and more specifically to the field of tomosynthesis. In particular, the present invention relates to the use of three-dimensional scan trajectories during acquisition of image data.
Tomosynthesis is an imaging modality that may be used, in a medical context, to allow physicians and radiologists to non-invasively obtain three-dimensional representations of selected organs or tissues of a patient. In tomosynthesis, projection radiographs, conventionally known as X-ray images, are acquired at different angles relative to the patient. Typically, a limited number of projection radiographs are acquired over a relatively small angular range. The projections comprising the radiographs generally represent the line integrals of the attenuation coefficients along the respective X-ray paths through the patient and, therefore, convey useful data regarding internal structures.
From the acquired projection radiographs, a three-dimensional representation of the imaged volume may be reconstructed. Typically, the reconstructed data set may be arranged in planar cross-sections, i.e., slices, of the volume at different heights, each slice being parallel to the plane of the X-ray detector. The reconstructed data set may be reviewed by a technologist or radiologist trained to generate a diagnosis or evaluation based on such data. In such a medical context, tomosynthesis may provide three-dimensional shape and location information of structures of interest as well as an increased conspicuity of the structures within the imaged volume.
The quality of the three-dimensional rendering available for viewing may depend, in large part, on the quality of the acquired projection data. For objects that are small relative to the size of the detector, the quality of the projection data, in turn, is generally limited by the range of angles over which the projection data is acquired. Therefore, the quality of the acquired projections typically depends, at least in part, on the scan trajectory traveled by the X-ray source during acquisition of the projection image data.
One-dimensional, i.e., linear scan trajectories, and two-dimensional, i.e., planar, scan trajectories yield a specific depth resolution, i.e., the resolution in the direction perpendicular to the detector surface, which is reflected in the subsequent three-dimensional rendering. In particular, for one-dimensional and two-dimensional scan trajectories, the depth information is defined by the scanning angles and is specific to each trajectory. Because depth resolution is limited by the available range of motion of the X-ray source, the depth resolution may not be as good as the resolution in the plane parallel to the detector surface. A technique for acquiring projection images during tomosynthesis that provides improved depth resolution may, therefore, be desirable.